The solar system formed from a cloud of material known as the solar nebula. The trigger for the collapse of the solar nebula into the solar system is thought to have been the explosion of a nearby supernova just over 4.6 billion years ago. The material remaining after formation dissipated when the Sun passed through the T Tauri phase.

Astronomy and Physics Terms by ExploreSpace.com

The large cloud of gas and dust from which the Sun and planets condensed 4.6 billion years ago.